Foam-producing process and material for acid metal-cleaning baths



Patented May 13, 1930 UNITED STATES PATENT OFFICE JAMES H. GBA VELL, OF ELKINS PARK, PENNSYLVANIA, ASSIGNOR TO AMERICAN CHEMICAL PAINT COMPANY, OF AMIBLER, PENNSYLVANIA, A CORPORATION OF DELAWARE FOAM-PRODUCING PROCESS AND MATERIAL FOR ACID METAL-CLEANING- BATH S No Drawing. Application filed new. 29, 1927,

This invention relates broadly to the art of foam production and specifically to the foam produced on acid baths that emit hydrogen.

The objects of the invention are to produce a more permanent foam on acid baths that emit hydrogen; to reduce the cost of foam production; to reduce the heat emanating from the bath; to save acid; to increase the efiiciency of the foam and to prevent the escape of acid spray from the bath.

Wheniron and steel are subjected to the action of an acid bath, such as a dilute solution of sulphuric acid, the acid attacks the metal and liberates hydrogen which bubbles up through the solution and escapes to the air. In so doing, the escaping hydrogen forms unstable bubbles on the surface of the bath, which in breaking, throw an acid mist or spray into the air, to the great detriment of health and materials in the vicinity.

In order to overcome this obnoxious condition, it is the custom to addto the bath a foaming agent, such as saponin, saponin-like materials, rye meal liquor and the like, cellulose pulp waste, etc., which acts to make the bubbles stable, and consequently causes thebath to cover itself with a blanket of foam,

which holds the escaping hydrogen long enough to allow its moisture to be precip1- tated back into the bath eliminating the acid maintain a permanent foam, the operator" must continually watch the bath and add the agent as conditions require. It should be noted that in the aggregate, so much of the foaming agent is required, that to add the entire amount when the bath is started, would so alter the proportions of the bath that in many cases it would not serve the purpose for 1 which it was intended. The care and atten tion required to maintain the proper foam on the bath depends so much on human nature that it is often neglected and hence the ob- Serial No. 179,389. Renewed. March 20,1930.

up, without danger of harming the bath, and

yet produce a satisfactory foam during the life of thebath.

The best foam protecting material known to me at the present time is formaldehyde,

paraformaldehyde, and those materials capa-- ble of generating formaldehyde in an acid bath in the presence of metal, such as thioamides and substituted thioamides (all these classes being hereafter included in the term thioamides). The thioamides work well with all the foaming agents but from a commercial aspect, I prefer that foaming agent known as cellulose pulp waste liquor.

To practice my invention I may make up an acid bath in a vat using v Gallons Water 1000 Sulphuric acid (66 B.) L 50 Into this bath there may be placed a ton of steel sheets to-be cleaned. The bath may be maintained at a temperature of 180 F.-

dgo this bath containing the steel, I may a Cellulose pulp waste liquor .50 gallons Thiocarbanilide 2.00 pounds the materials referred to above, produces a 7 suitable blanket of foam that endures until the acid isexhausted.

All other conditions being equal, a bath operated without my foam protector would require constant additions of the foaming agent so that in the aggregate itwould amount to ten times as much or more.

My invention therefore acts to conserve the foaming agent and to materially reduce the attention the bath requires to maintain the blanket of foam.

For convenience the foaming agent and the foam protecting material may be compounded in advance and this admixture added to the bath instead of the simple foaming agent. In this case I prefer to use the evaporated cellulose pulp waste liquor which isa solid and I may compound the ingredients as follows Pounds Evaporated cellulose pulp Waste liquor- 2.00

Thiocarbanilide; 2 00 This results in a powder admixture, insufficient amount to treat the bath which I have described above.

Although I am unable to propose a philosophy to account for the surprising result of materially increasing the longevity of the foam, I am convinced that the presence of the formaldehyde accounts in some unknown manner for it.

The following is a definition of thiomide:

where R and R represent hydrocarbon radicals or hydrogen, and R represents hydrogen,

a hydrocarbon radical, an amino group or a substitute amino group.

It will be obvious to those skilled in the art that the invention is of chemical character, hence I claim the benefit of equivalents appropriate in such cases.

I claim:

1. A bath for pickling metal comprising a metal etching acid and water, and further comprising a reaction controlling agent capable of generating formaldehyde in insuflicient'quantity to stop the generation of hydrogen, and cellulose Waste liquor.

- and a foam producin a ent.

JAiiE 2. A bath for pickling metal comprising a metal etching acid and water, and further comprising a thioamide body in insuflicient quantity to stop the generation of hydrogen, and a foam producing agent.

3. A bath for pickling metal comprising a metal etching acid and Water, and further comprising thiocarbanilide in insuflicient quantity to stop the generation of hydrogen,

I-I. GRAVELL. 

